Concentric conductor electric cable



Aug. 30, 1949. E. BAGULEY CONCENTRIC CONDUCTOR ELECTRIC CABLE 2 Sheets-Sheet 1 Filed Aug. 2, 1946 r1 Hurney Aug. 30, 1949. E. BAGULEY CONCENTRIC CONDUCTOR ELECTRIC CABLE 2 Sheets-Sheet 2 Filed Aug. 2, 1946 A Horny) Patented Aug. 30, 1949 CONCENTRIC CONDUCTOR ELECTRIC CABLE Eric Baguley, London, England, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application August 2, 1946, Serial No. 687,821 In Great Britain June 11, 1945 Section 1, Public Law 690, August 8, 1946 Patent expires June 11, 1965 4 Claims.

This invention relates to concentric conductor cables.

It has previously been proposed in British patent specification 476,098 to construct the outer hollow conductor of such a cable from a metal tape formed into a tube with the edges of the tape abutted together to form a seam, each edge of the tape having projections thereon overlying the outer side of the other edge.

When the diameter of the outer conductor exceeds a particular limit, it becomes uneconomical to use a single metal tape folded into a tube in this way and according to one feature of the present invention the outer conductor is built up of a plurality of metal tapes abutted together longitudinally to form seams, each edge of each tape being provided with projections interengaging with projections on the adjacent edge of another tape to hold the edges in abutting relation. Preferably the projections on each edge overlie the outer side of the adjacent edge.

when the diameter of the outer conductor is increased beyond a certain limit, in order to transmit with small attenuation a wider frequency band, the diameter of the inner conductor becomes sufiici'ently large as to make it advisable to construct the inner conductor also as a hollow conductor and some constructions of this kind both for solid and air spaced concentric conductor cables are described in copending British patent application No. 11,723 of 1945.

In cases in which both inner and outer conductors consist of hollow tubes, it is preferable according to the present invention to construct both conductors from tapes of similar dimensions to facilitate manufacture, e. g, the centre conductor may comprise one of such tapes formed into a tube, and the outer conductor form such tapes abutted together longitudinally, the projections on each edge of the tape forming the inner conductor underlying the projections on the adjacent edge so that the inner conductor presents a smooth outer perimeter.

According to another feature of the present invention an inner conductor in the form of a tube is supported within the outer conductor by means of a plurality of interengaging slotted strips of insulating material running parallel to the axis of the mid inner conductor and lying tangentially to the outer surface of said inner conductor, and engaging the inner surface of the outer conductor.

The invention will be better understood from the following description of two embodiments thereof taken in conjunction with the accompanying drawings in which Fig. 1 shows a transverse cross-section of the core of a concentric conductor cable according to the invention.

Fig. 2 is a side elevation of the core of Fig. 1 with part of the outer conductor cut away.

Fig. 3 is a transverse cross-section of the core of an alternative form of concentric conductor cable according to the invention.

Fig. 4 is a view of one of the insulating strips used in the construction of Figs. 1 and 2 or of Fig. 3.

Referring to the drawings, Figs. 1 and 2 show the inner and outer conductors of a concentric conductor cable according to the invention. The requirement to be met is that the internal diameter of the outer tubular conductor l is to be 0.975 inch or 24.8 mm. For copper conductors the outer diameter of the inner conductor 2 should be 0.27 inch or 6.9 mm. to preserve the optimum ratio of 3.6 between the diameters of the conductors, from the point of view of ensuring the widest transmission band for a given attenuation. A solid copper wire of 0.27 inch or 6.9 mm. for

the inner conductor is uneconomic and scarcely practicable for other considerations. The inner conductor 2 is accordingly made as a hollow copper tube made by folding longitudinally a. single copper tape having projections along its edges so that the projections along the two edges interengage, those on one edge underlying those on the other edge so that the projections are on the inside of the formed tube, as shown at 3 and as described in British patent specification No. 11,723/45.

If the outer conductor l were to be made in the same manner or in the manner described in British patent specification 476,098 from a single folded tape, a tape of 3.2 inches or 81.3 mm. in width would be required, which is not advisable for cables required to be made in lengths of up to 350 yards or 330 metres without joints in the outer tube. 0n the other hand it is desirable to avoid the attenuation instability which results if the conductor l were to be made up of short lay spiral tapes. According to the invention, therefore, the outer conductor I is formed from three or four longitudinally applied notched tapes each 1.03 inches (26.2 mm.) or 0.775 inch (or 19.7 mm.) wide by 0.01 inch (0.25 mm.) to 0.015 inch (0.38 mm.) thick. In Figs. 1 and 2 the outer conductor is formed of four tapes I each 0.775 inch (19.7 mm.) wide.

It is to be noted that in calculating the width 3 of tape required in any particular case account must be taken of the fact that the tapes must first be fed into a punch press wherein the teeth or projections along the edges are formed before the tape or tapes can be formed into the shape of a hollow conductor.

A single tape 0.775 inch (19.7 mm.) wide of 0.01 inch (0.25 mm.) thick can be formed into the central conductor 2 giving a tube of external diameter 0.255 inch (6.5 mm.) which as central conductor to the 0.975 inch (24.8 mm.) tube gives a D/d ratio of 3.82. The effect of displacing this ratio from its optimum value of 3.82 is to increase the ratio frequency attenuation of the cable by only 0.15% and to increase the impedance by 4%. There is thus no serious objection to the step of facilitating the manufacture of the cable by using tape of the same size both for the inner conductor 2 and to build up the outer conductor I, one tape being used for the former and four for the latter. Moreover by using tapes thicker than 0.01 inch (0.25 mm.) the D/d ratio of the outer conductor i and inner conductor 2 may be brought nearer to the optimum value of 3.6, and when the tape thickness is of the internal diameter of the tube constituting the outer conductor the D/d ratio is reduced to that figure. Thus for an outer conductor of 0.975 inch or 24.8 mm. internal diameter the tape thickness to ensure this ratio with the construction shown is 0.022 inch or 0.51 mm. approximately, though thinner tapes give sufliciently robust tubes and it may not be considered essential for the reasons given, to use tape of this thickness.

The inner conductor 2 may be lapped with a thin tape of insulating material (not shown) such as polythene or covered with a thin extended coating of polythene to keep the longitudinal seam closed until the spacers about to be described are applied thereto.

The inner conductor 2 is maintained concentrically within the outer conductor l by means of three slotted strips 5 of thin insulating material such as polystyrene parallel to the axis of the central conductor 2 and lying tangentially along its outer surface as shown in Fig. 1, with an angle of 60 between each pair of strips. The slots in the strips are cut as shown in Fig. 2 and are disposed so that the slots in one of the strips permit the projecting teeth on the adjacent edge of another strip to pass through. The depth of the slots and projecting teeth is such that the outer edges of the teeth just meet the inner surface of the outer conductor I. The teeth and slots are dimensioned so that the teeth fit tightly into the slots and the three interengaging strips 5 form a self supporting structure around the inner conductor 2 over which the outer conductor l' is applied.

The cable is completed in well-known manner by applying any suitable or well-known lapping to the exterior of the outer conductor I. Thus a double lapping of steel tapes may be applied in short lay open helices breaking joint in the manner at present known in the construction of concentric conductor cables. Instead of being exactly longitudinal the tapes 4 may be laid up with a comparatively long lay of not less than about 56 inches or 143 cm. A somewhat shorter lay is possible provided a short lay helix of copper tape is applied to the outer conductor I before applying the above mentioned steel tapes in order to screen these tapes from the spiral gap in the outer conductor. The core may then be completed if desired by a thin walled tube of insulating material extruded over the screening tapes.

The insulating strips 5 may be applied in long or short lengths according to their thickness and thus according to the stlflness thereof. If the strips are comparatively stiff they may take the form shown in Fig. 4 and be provided at one end with a dove-tail notch 6 and at the other end with a correspondingly shaped projection I so that strips contiguous in length may be fitted together to form in eflect a continuous strip. The strips may also have holes 8 punched out therefrom to reduce the amount of solid material in the coaxial core.

Fig. 3 shows another embodiment of the invention in which four insulating strips 5 are built up into an interlocking self supporting structure around the inner conductor 2, the strips 5 being at to one another. The core shown in Fig. 3 is completed in the same manner as described above.

The central conductor 2 may support an inner solid conductor spaced therefrom or additional conductors may be provided within the hollow conductor 2 as described in British patent application No. 11,723/45.

What is claimed is:

l. Concentric conductor cable having an inner conductor in the form of .a tube supported within a concentric outer conductor by means of a plurality of interengaging slotted strips of insulating material running parallel to the axis of the said inner conductor, lying tangentially to the outer surface of said inner conductor and engaging the inner surface of the outer conductor.

2. Concentric conductor cable as claimed in claim 1 having three said strips of insulating material at 60 to each other.

3. Concentric conductor cable as claimed in claim 1 having four said strips of insulating material at 90 to each other.

4. Concentric conductor cable as claimed in claim 1 wherein said strips are built up longitudinally of short interengaging strips.

ERIC BAGUIEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain Oct. 31, 1938 

